WMOD00390

• Title: A Proposed Wintertime Weather Modification Research Program for Colorado
• Date: 1/1/1980
• State: CO
• Weather Modification - Doc Type: Report

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should be completed to deterlnine precipitation changes over the
total primary program area that was shown in Figure 8. Secondly,
a similar type of evaluation shou~d be completed over the portion
of the primary area most likely to be affected by seeding. In
Section IV.b.3 it was stated that the northern portion of the
primary area (Pl) favors sou,thwest flow precipitation episodes
while the southern half (P2) favors northwest flow precipitation
episodes. It is possible to have both flow situations occur
during different stages of the same weather event; for example,
initial flow could be from the southwest with flow changing to
the northwest following the passage of a mid-level pressure trough.
For the first type of evalua1:ion the entire primary area would be
considered as a unit for the duration of the event. The second
type of evaluation would divide the event at the time of trough
passage (as determined from program rawinsonde data), This second
type of evaluation also becornes important when only portions of
the primary target area can be effectively seeded because of
marginal wind directions for the established generator network
or operational aircraft flight paths upwind of the area.
Different types of evaluation techniques may be utilized
such as seeded inter-basin comparisons of precipitation and
runoff with current data and historical data,-comparisons of
similar basins (one seeded and one not seeded) in their precipita-
tion and runoff amounts, comparison of computer model outputs for
natural and seeded amounts for the seeded region and nearby un-
seeded region with actual precipitation observations in both the
seeded and unseeded areas, and a statistical comparison of ran-
domly seeded and unseeded similar weather events.
The evaluation for seedi.ng effects would be based on hourly
precipitation accumulations reduced from the surface recording
precipitation gage network. The strongest statistical tests
available for comparing randomized seeded and non-seeded data sets
would be utilized. These sta.tistical analyses should test the
hypothesis that cloud seeding' utilizing the methods proposed
increases winter precipitation within the target area. As was
stated in Section IV.B.2.e, t.he cumulative precipitation during

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